1. Field of the Invention
This invention pertains to a novel cyclodehydration reaction which produces 2-oxazolines using iron-containing compounds as the catalyst.
2. Description of the Prior Art
The 2-oxazolines are a known class of compounds whose chemistry has been summarized by Wiley et al., Chemical Reviews, Vol. 44, 447-476 (1949); Seeliger et al., Angew. Chem. International Edition, Vol. 5, No. 10, 875-888 (1966), and Frump, Chemical Reviews, 1971, Vol. 71, No. 5, 483-505. Patents and other references pertaining to monomeric 2-oxazolines have normally been classified by the U.S. Patent and Trademark Office under the classification 260/307F.
The 2-oxazolines correspond to the general formula ##STR1## wherein R is hydrogen, hydrocarbyl or inertly-substituted hydrocarbyl, and R.sub.1 -R.sub.4 are each independently hydrogen, hydrocarbyl, or an inertly-substituted hydrocarbyl group. The best known oxazolines are those in which R is hydrogen, alkyl or phenyl and R.sub.1 and R.sub.2 are hydrogen, lower alkyl or hydroxymethyl or derivatives thereof (e.g., esters) and R.sup.3 and R.sub.4 are each hydrogen.
2-H-2-Oxazoline is the first member of the oxazoline series and is the "simplest" molecule. It corresponds to formula II. ##STR2## The 2-H2-oxazolins and particularly II above are generally quite different from the corresponding 2-substituted-2-oxazolines. This is illustrated by the fact that many conventional processes for preparing 2-substituted-2-oxazolines are not particularly satisfactory for the preparation of the corresponding 2-H2-oxazolines. For example, many 2-substituted-2-oxazolines are conventionally prepared by dehydrochlorinating an N-(.beta.-chloroalkyl)carboxamide with aqueous alkali. Compound II, on the other hand, is produced by this process in only very low yields and is accompanied by decomposition of the desired product. H. Wenker, J. Am. Chem. Soc., 60, 2152 (1938).
Another common technique for preparing 2-oxazolines is the cyclodehydration of N-(.beta.-hydroxyalkyl)carboxamides over various catalysts. Litt et al. (U.S. Pat. No. 3,681,329 and U.S. Pat. No. 3,681,333) claimed that 2-H-2-oxazolines could be prepared by contacting the appropriate formamides with compounds of manganese, cobalt, molybdenum, tungsten and the rare earth metals. Unfortunately, there is no experimental data in Litt et al. which would substantiate this allegation. Hess teaches in Canadian Pat. No. 536,594 and British Pat. No. 758,972 that II can be prepared by a cyclodehydration of N-(2-hydroxyethyl)formamide in the presence of a dehydrating agent (specifically diatomaceous earth, sulfuric acid, aluminum oxide and iron oxide). The yields reported by Hess were higher than the yield reported by Wenker but were still rather low and commercially unsatisfactory. In contrast to this, Litt et al. teach in U.S. Pat. No. 3,562,263 that 2-substituted-2-oxazolines are prepared in excellent yield by cyclodehydration of N-(2-hydroxyalkyl)carboxamides over aluminum oxide.
In view of these differences between 2-H2-oxazolines and 2-substituted-2-oxazolines in the various methods of preparation, it was surprising to find a class of compounds which would catalyze the cyclodehydration of N-(2-hydroxyethyl)formamides and carboxamides to form the corresponding 2-H2-oxazolines or the 2-substituted-2-oxazolines.